Erythropoietin (EPO) is a hormone found in the plasma which regulates red cell production by promoting erythroid differentiation and initiating hemoglobin synthesis. The gene is in the EPO/TPO family and encodes a secreted, acidic glycosylated cytokine.
Recombinant human erythropoietin (EPO) has been used since 1986 to treat the anemia of chronic and end-stage kidney disease (Eschbach, et al., N. Engl. J. Med. 1987 Jan. 8; 316(2):73-8). However, this treatment is costly and requires parenteral administration. It has recently been linked to cardiovascular side effects (J. Bohlius et al., Lancet 373, 1532 (2009) and antibodies which form against EPO can result in Pure Red Cell Aplasia (PRCA), an uncommon condition which develops in association with a failure of the bone marrow to manufacture red blood cells, leaving patients with severe, treatment-resistant anemia (reported by Casadevall, et al, New England Journal of Medicine, Feb. 14, 2002).
In addition to its role as a kidney cytokine regulating hematopoiesis, EPO is also produced in the brain after oxidative or nitrosative stress. The transcription factor HIF1 (hypoxia inducible factor 1) is known to upregulate EPO following hypoxic stimuli (Digicaylioglu, M., Lipton, S. A. Nature 412: 641-647, 2001). This upregulation provides protection against apoptosis of erythroid progenitors in bone marrow and also apoptosis of brain neurons (Siren, A.-L., et al., Proc. Nat. Acad. Sci. 98: 4044-4049, 2001). Grimm et al. showed in the adult mouse retina that acute hypoxia dose-dependently stimulates expression of EPO, fibroblast growth factor-2, and vascular endothelial growth factor via HIF1 stabilization (Nature Med. 8: 718-724, 2002).
Further controlling the regulation of EPO production are a family of prolyl hydroxylases, the PHD proteins, which act to regulate the HIF transcription factors. PHD (prolyl hydroxylases) proteins belong to a superfamily of several 2-oxoglutarate-dependent dioxygenases (Kaelin Jr., and Ratcliffe, Mol. Cell. 30, 393 (2008). In the mouse, these genes are known as EGLN1 (PHD2, prolyl hydroxylase domain-containing protein 2 and by the synonyms hif-prolyl hydroxylase 2; hifph2; hph2; chromosome 1 open reading frame 12; c1orf12; sm20, rat, homolog of sm20; zinc finger mynd domain-containing protein 6; and zmynd6), EGLN2 (PHD1, prolyl hydroxylase domain-containing protein 1; and by the synonyms hif-prolyl hydroxylase 1; hifph1) and EGLN3 (PHD3 prolyl hydroxylase domain-containing protein 3; and by the synonyms hif-prolyl hydroxylase 3; hifph3). In an attempt to elucidate the function of PHD enzymes in hepatic EPO production, Minamishima et al., created knockout mice lacking liver expression of PHD1, PHD2, PHD3, or combinations thereof (Mol. Cell. Biol. 29, 5729 (2009)).
Subsequent studies by Minamishima and Kaelin using the knock-out model, suggested that while hepatic inactivation of PHD1, PHD2, or PHD3 alone did not increase EPO or hematocrit values, loss of all three PHDs increased both measurements (Science, 329, 407 and Supplemental Information (2010)). According to Minamishima, questions remain regarding the promoters used and the role that PHD2 plays (and at which developmental stage) independent of the other two enzymes in the activation of EPO production.
Double-stranded RNA molecules (dsRNA) have been shown to block gene expression in a highly conserved regulatory mechanism known as RNA interference (RNAi). This natural mechanism has now become the focus for the development of a new class of pharmaceutical agents for treating disorders that are caused by the aberrant or unwanted regulation of a gene.
Given the drawbacks of complete gene knockout and the inherent problems translating gene knockout to human therapy, the present invention contemplates the use of RNAi to effect gene modulation with improved outcomes in the production of erythropoietin.
During development the liver is the major source of EPO but over time eventually the liver EPO is switched off and in normal healthy adults their kidney makes the EPO to support normal red blood cell production. However, two to four million Americans with renal disease suffer from anemia due to impaired EPO production. If it is possible to turn on hepatic EPO using siRNA targeting EGLN genes the liver could now supply the EPO required to support red blood cell production to compensate for the damaged kidney function. Furthermore, using siRNA in LNPs it may be possible to activate fetally expressed genes in liver by targeting negative regulators of the pathway. This strategy could be used in the treatment of many other diseases and not just exclusively anemia.